A complete AR lower is the part of an AR-15 rifle that the federal government legally classifies as the "firearm" itself

When you buy an AR-15, the lower receiver is the serialized metal piece that the law treats as the gun. A complete lower means it comes fully assembled with the trigger group, safety selector, magazine catch, and stock already installed — ready to attach an upper receiver and fire. A stripped lower is just the metal frame with none of those parts, which is why it is often cheaper but requires you to assemble the trigger mechanism yourself.

The distinction matters because federal law regulates the lower receiver as the firearm, not the barrel or bolt. That is why you can order an upper receiver online and have it shipped to your door, but a lower receiver must go through a licensed firearms dealer (FFL) and a background check, whether it is complete or stripped.

Key Takeaways

  • A complete lower receiver comes with the trigger group, safety, magazine catch, and stock already assembled, so you only need to attach an upper receiver to have a working rifle.
  • The lower receiver is the part the federal government legally defines as the firearm, which is why it requires a background check and an FFL transfer regardless of whether it is complete or stripped.
  • A complete lower costs more than a stripped lower but saves you the time and tools needed to assemble the trigger mechanism and other internal parts.
  • State and local laws vary widely on what you can own, how you can modify it, and whether you need a permit, so you must check your own jurisdiction before purchasing.

Why the lower receiver is the regulated part

The lower receiver is the part that holds the trigger, hammer, and firing pin — the mechanism that actually fires the round. Because it controls when the gun fires, federal law treats it as the firearm itself. The upper receiver, barrel, bolt, and charging handle are all legally considered parts, not firearms, which is why they are not serialized and do not require a background check to purchase.

This legal distinction is why you will see complete lowers sold at gun shops and sporting goods stores alongside other firearms, but you will also see stripped lowers sold online by parts suppliers. Both routes require an FFL transfer, but the stripped lower is cheaper because you have to do the assembly work yourself.

What comes installed on a complete lower

A complete lower receiver includes the trigger assembly (the trigger and hammer), the safety selector, the magazine catch (the button that releases the magazine), the pistol grip, and usually the stock or buffer tube. Some complete lowers come with a fixed stock, while others have a collapsible stock that slides along a buffer tube. A few come with just the buffer tube, leaving the stock choice to you.

The trigger pull weight and type vary by manufacturer and price. Budget complete lowers often have a heavier, grittier trigger that breaks at 7 to 8 pounds of pressure. Mid-range and higher-end lowers may have a cleaner trigger that breaks at 4 to 6 pounds. If you plan to shoot competitively or want a lighter trigger, you can always replace the trigger group later, but a complete lower gets you functional right away.

Complete lower versus stripped lower: cost and effort

A complete lower typically costs between $100 and $300 depending on the brand and trigger quality. A stripped lower usually costs $50 to $150. The difference is that a stripped lower requires you to buy and install a trigger group separately, which adds $50 to $200 to the final cost and requires basic gunsmithing tools and knowledge.

If you are building your first AR-15, a complete lower removes one major assembly step. You can focus on assembling the upper receiver (which is simpler) and then mate the two together. If you are an experienced builder or want to customize the trigger, a stripped lower gives you more control over which components go into your rifle.

How to purchase a complete lower

You can buy a complete lower from a licensed firearms dealer in your state. This includes gun shops, sporting goods stores that have a firearms counter, and some online retailers that operate as FFLs. You cannot have a complete lower shipped directly to your home — it must be shipped to an FFL, who will conduct a background check before you take possession.

The background check process is the same as buying any other firearm. You will fill out a federal Form 4473, provide a government-issued ID, and wait while the dealer contacts the National when ready Criminal Background Check System (NICS). The check usually takes a few minutes, though it can take up to three business days in some cases. If you pass, you pay for the lower and take it home. If you fail, the dealer will not release it to you.

Some states require additional steps, such as a state-specific background check, a waiting period, or a permit to purchase. A few states require registration of the lower receiver itself. You must check your state and local laws before you buy, because what is legal in one state may be prohibited in another.

State and local laws that affect complete lowers

Federal law treats all AR-15 lowers the same way, but state and local governments add their own rules. Some states ban AR-15s entirely or ban certain features like adjustable stocks or pistol grips. Others require you to register the lower with the state police. A few states have different rules for lowers with certain features — for example, a lower that accepts a magazine with more than a certain capacity might be restricted.

California, New York, Connecticut, and a few other states have specific restrictions on AR-15 features or require registration. Some cities within otherwise permissive states have their own bans. Before you purchase a complete lower, search your state's firearms laws or contact your local police department's firearms licensing unit to confirm what you can legally own and whether you need a permit.

Attaching an upper receiver to your complete lower

Once you have a complete lower, you need an upper receiver to make a working rifle. The upper receiver is the barrel, bolt, charging handle, and handguard assembly. You can buy a complete upper receiver (fully assembled) or a stripped upper (just the receiver and handguard, requiring you to install the barrel and bolt yourself).

Mating the upper and lower is straightforward: you align the two pieces and insert two takedown pins through the holes that connect them. No tools are required. The upper and lower do not have to be the same brand — an upper from one manufacturer will work with a lower from another. This modularity is one reason the AR-15 platform is popular: you can swap uppers to change caliber or configuration without buying a whole new lower.

Frequently Asked Questions

Do I need a background check to buy a complete lower?

Yes. A complete lower is classified as a firearm under federal law, so it must be transferred through a licensed firearms dealer and requires a background check. This is true even if you buy it online — it must be shipped to an FFL in your state, where the check happens before you take possession.

Can I buy a complete lower online and have it shipped to my house?

No. A complete lower must be shipped to a licensed firearms dealer (FFL), not to your home. You then go to the dealer, pass a background check, and take possession there. The dealer charges a transfer fee, usually $25 to $75, for this service.

What is the difference between a complete lower and a complete rifle?

A complete lower is just the lower receiver with the trigger group and stock installed. A complete rifle has both the lower and upper receiver assembled and ready to shoot. A complete lower still requires you to buy and attach an upper receiver before you have a working rifle.

Can I modify a complete lower after I buy it?

Yes, you can replace the trigger group, stock, or pistol grip with aftermarket parts. However, some states restrict certain modifications — for example, adjustable stocks or high-capacity magazine compatibility. Check your state and local laws before you modify, because some changes may make your rifle illegal to own in your jurisdiction.

Why is a stripped lower cheaper than a complete lower?

A stripped lower costs less because you have to buy and install the trigger group yourself. The trigger group is the most complex part to assemble, requiring small springs, pins, and careful alignment. A complete lower includes this work, so you pay more upfront but save time and the cost of buying the trigger group separately.